The present invention relates to a fuel injection pump for a diesel engine, and more particularly relates to a diesel fuel injection pump in which fuel spilling is controlled at the stoppage of the engine for the readiness of the restarting, and in which venting of the split fuel is performed by recirculating it.
There is known a type of fuel injection pump or a diesel internal combustion engine which includes a plunger which reciprocates to and fro in a bore defined in a housing, a high pressure chamber being defined between one end of the plunger and the end of the bore. During the suction stroke of the plunger as this high pressure chamber expands in size, diesel fuel is sucked into this high pressure chamber from a quantity of diesel fuel contained in a relatively low pressure chamber, through a fuel supply passage; and during the compression stroke of the plunger as the high pressure chamber subsequently contracts in size, this diesel fuel in the high pressure chamber is squeezed and is brought to a high pressure and is ejected through an injection passage therefor to a fuel injector of the diesel internal combustion engine. Sometimes, in the case that the diesel fuel injection pump is a so called distribution type pump, the plunger is rotated as it reciprocates, and by a per se well known construction the spurt of highly compressed diesel fuel is directed to the appropriate one of the plurality of cylinders of the internal combustion engine.
Now, in order to ensure that the diesel engine is definitely and positively stopped from operation when it is desired to do so, it is known to provide an electromagnetic valve for fuel cutoff, which, when the master operation switch of the vehicle in which the engine is mounted (the so called ignition switch) is switched off, definitely interrupts the flow of fuel from the aforementioned relatively low pressure chamber, through a fuel supply passage; when this happens, the diesel engine comes to a halt quite quickly due to shortage of fuel.
However, a problem has occurred with this construction, as follows. Such an electromagnetic valve for fuel cutoff typically comprises a valve seat with a hole therethrough interposed at an intermediate point on the aforementioned fuel supply passage, and a valve element, which is displaced from said valve seat when fuel flow through said fuel supply passage is desired, i.e. when the engine is running, and is pressed against said valve seat so as to close said hole therethrough when fuel flow through said fuel supply passage is not desired, i.e. when the engine is to be stopped. Typically, also, the direction of fuel flow through said hole of said valve seat is in the direction from the side of said valve seat on which said valve element is located, through said hole, towards the other side thereof. Now, if the diesel engine is to be stopped from operation, then as mentioned above the valve element of said electromagnetic valve for fuel cutoff approaches the valve seat and closes its hole, and thus the part of the fuel supply passage downstream of the electromagnetic valve for fuel cutoff is isolated from the upstream part thereof, and fuel flow is prevented. Thus the diesel engine, being deprived of fuel, slows down and stops rotating. However, the diesel engine does continue to rotate for a few seconds or so, and the pumping action of the plunger, which is trying to suck fuel out of said part of the fuel supply passage downstream of the electromagnetic valve for fuel cutoff and to eject it via said electromagnetic fuel amount control valve and via its vent passage to the outside, by succeeding in thus sucking an extremely small amount of fuel (since the fuel is not completely incompressible, and the metallic parts of the pump deform very slightly), causes a substantial negative pressure to be built up in said downstream part of said fuel supply passage. Now, if the diesel engine is left for a long time before any attempt is made to restart it, then through natural leakage this negative pressure becomes gradually cancelled, and no problem is thereby caused. However, if an attempt is made to restart the diesel engine quite quickly, then this negative pressure in the part of the fuel supply passage downstream of the electromagnetic valve for fuel cutoff can forcibly suck the valve element of said valve against the valve seat and can maintain said electromagnetic valve for fuel cutoff closed, even though the control system for the fuel injection pump is attempting to open it electrically. If this happens, the diesel engine is prevented from restarting.
Particularly, this problem is most likely to occur if, while the vehicle is being driven along the road, the master control switch is erroneously switched by the operator of the vehicle to the off position. When this happens, the electromagnetic valve for fuel cutoff is as described above closed by the control system, and because the engine is forcibly kept rotating at a considerable rotational speed by the running of the vehicle along the road and thus the engine rotational speed does not drop, the previously explained negative pressure generated in the portion of the fuel supply passage downstream of the fuel cutoff valve is particularly severe, and does not diminish, thus presenting a very great likelihood of its holding the fuel cutoff valve closed, even when the operator of the vehicle, recognizing his or her mistake, turns the master control switch back to the on position in an effort to rectify the error and to continue operating the vehicle. In such a case, the vehicle is constrained to come to a complete halt, due to this effect of the negative pressure holding the fuel cutoff valve closed.
An expedient that might be thought of for preventing this problem is to increase the size and the power of the components of the electromagnetic valve for fuel cutoff, thus overcoming the suction force described above by main force; but this is not completely effective, and moreover means increasing the size and the weight and the cost of the electromagnetic valve for fuel cutoff and therefore of the fuel injection pump as a whole. Accordingly this solution is not a good one.